1. Field
An embodiment of the present invention relates to a projection optical system, exposure apparatus, and device manufacturing method.
2. Description of the Related Art
The photolithography process for manufacture of the semiconductor devices and others is carried out using an exposure apparatus for projecting a pattern of a mask (or a reticle) through a projection optical system onto a photosensitive substrate (a wafer or a glass plate coated with a photoresist, or the like). The ordinary exposure apparatus is arranged to form one type of pattern image in one shot area (unit exposure region) on the photosensitive substrate.
In contrast to it, in Japanese Patent Application Laid-open No 2000-21748, the exposure apparatus proposed for improvement in throughput is one using a double exposure method for superimposing two types of patterns in one shot area on the photosensitive substrate to form one synthetic pattern.